A quick hypertext drive: Prior to 1980, the western I-84 was numbered as I-80N (“80 North”), as though it were a “child” route breaking away from mainline I-80 in Utah; this bit of history explains the apparent numbering violation of having I-82 north of I-84 in Oregon and Washington. In 1980, the American Association of State Highway and Transportation Officials (AASHTO) decided to eliminate suffixed Interstate designations, and created a western I-84 designation, matching the older one on the East Coast, to replace the old I-80N numbering.

West of Heyburn, ID, I have never been on the western I-84, and can give only a few of the most basic highlights. From the east side of Portland out to Boardman, OR, I-84 literally hugs the southern bank of the Columbia River, following the river through a deep gorge for much of that distance. East of Pendleton, near milepost 219, the highway begins a six-mile climb (if eastbound — a descent going west) up Emigrant Hill, with multiple 180° curves and a 2,000-ft. (610 m) elevation difference between the bottom and the top. Once over Emigrant Hill, I-84 turns to the south-southeast and heads through the High Desert area of eastern Oregon and southwestern Idaho, before eventually reaching the Magic Valley of south-central Idaho. The general elevation of much of I-84 east of Emigrant Hill is in the 4,000-ft. (1,219 m) range.

Interstate 84 in much of Idaho follows the general path of the Snake River, although west of Hammett, the highway and the river are not particularly close to each other. Finally, just east of Rupert, I-84 crosses to the south side of the Snake River, and several miles later, it spawns the western Interstate 86 for its short run to Pocatello, ID. Still staying in the Magic Valley for a bit, I-84 turns to the southeast at the I-86 split; about 20 miles southeast of I-86, I-84 begins a gentle climb to 5,530-ft. (1,686 m) Sweetzer Summit. Except for the first mile or so beyond the summit, the descent is equally gentle, and about 10 miles before the Utah border, I-84 is back down into flat country.

A little bit beyond Snowville, UT, I-84 enters into some fairly long and large rolling hills; none of these are horrendously steep, but a few are close to two miles long. Just a few miles before meeting Interstate 15 at Tremonton, I-84 enters the extreme northern end of the Great Salt Lake valley and becomes as flat as a billiards table. From Tremonton to the south side of Ogden, a distance of 39 miles, I-84 multiplexes on I-15 through mostly rural and semi-rural country — Ogden itself presents the first real urban/suburban surroundings in this area.

Eventually, I-84 resumes its own alignment along the south side of Ogden, with a few more exits in the city, before it enters the Wasatch Range east of the city. The alignment through the mountains follows the Weber River Canyon, and therefore isn’t very steep at all; rather, it winds around a bit, with some curves having a recommended speed of 55 mph (88 km/h). There is a fairly straight section that passes the city of Morgan, before I-84 enters one more winding section and eventually terminates upon reaching a “Y” interchange with Interstate 80.

Interstate 684 — 29 miles long; spur that “spears” I-84 (exists on both sides of I-84) and connects to the Hutchinson River Parkway at Purchase, NY for access to New York City; crosses I-84 at its own Exit 9; roughly one mile passes through Connecticut but is maintained by the New York State Department of Transportation (NYSDOT); I-84 Exit 20

Interstate 384 — 7½ miles long; spur from I-84 in East Hartford to U.S. Routes 6/44 near Bolton, CT; I-84 Exit 59

A quick hypertext drive: The eastern Interstate 84 serves at least two primary functions, one as a regional bypass of New York City for New England traffic, and the other as the main east-west artery of central Connecticut. As a result, backups in this area of Connecticut are commonplace during peak traffic times.

The highway begins at an interchange with Interstate 81 on the northeast side of Scranton, PA, in the suburb of Dunmore. It proceeds to the southeast, up a hill, for four miles before splitting from Interstate 380 and turning to the east. The rest of the length in Pennsylvania is spent transiting the Pocono Mountains, and although there are no tremendously steep grades, I-84 goes up and down quite a bit in this area. It finally flattens out a bit in the last couple of miles before the Delaware River crossing.

Interstate 84 just barely misses the state of New Jersey, literally by as little as 30 feet, crossing the Delaware River into New York. The first New York exit, which connects to New Jersey Route 23, is infamous for incorrect signage of that route; various signs have indicated it as a New York state route, and others have mistakenly added the letters “NJ” where they don’t belong to standard New Jersey state route shields. Shortly thereafter, I-84 begins a steep three-mile climb to 1,272-ft. (388 m) High Point, the highest point along the length of the highway, before descending again for a couple miles. (This is actually on the side of the feature that forms the highest point in New Jersey, a few miles to the south of I-84.)

After the descent from High Point, I-84 flattens out and crosses downstate New York, generally keeping 45-50 miles away from NYC. The Newburgh-Beacon Bridge, actually a pair of truss structures, charges only eastbound I-84 motorists a toll while allowing westbound traffic free passage. There are another couple of short, steep climbs and descents in Dutchess County, NY, and several more west of Waterbury, CT, but most of I-84 from there to Hartford is mildly or moderately rolling. Climbing lanes are provided on most of the hills, and there are six- or even eight-lane sections in Danbury and Waterbury.

After Interstate 691 splits from I-84 near Southington, CT, I-84 turns almost to due north and passes near Bristol and New Britain, before turning to the northeast to approach Hartford. Most of this part of I-84, and in fact much of I-84 from here on east, is six lanes. Several tight curves west of downtown Hartford necessitate the lowering of the speed limit to 50 mph (80 km/h) through the city. Just before the I-91 interchange, which lacks a direct ramp from I-84 westbound to I-91 southbound, I-84 passes through a short cut-and-cover tunnel in downtown Hartford; this stretch is eight lanes wide except right through the I-91 interchange.

East of Hartford, I-84 narrows back to six lanes and heads mostly northeast into hilly terrain. There are comparatively few exits (vs. west of and inside Hartford) in what remains of Connecticut. Eventually, eight miles into Massachusetts, I-84 turns into a giant on-ramp to Interstate 90/Massachusetts Turnpike, and traffic that doesn’t exit I-84 at U.S. Route 20 must enter the Masspike at its Exit 9. For long-distance traffic that has used I-84 to bypass NYC on the way to New England, Boston is 56 miles (90 km) east of the terminus of I-84.